An ink jet device comprising a line ink jet head of this type is taught, for example, in Japanese Examined Patent Application (kokoku) 3-58917. An ink jet device as taught in the cited application comprises a line ink jet head having a plurality of ink jet head units, each having a plurality of ink nozzles, arranged in series in line with the ink nozzle arrangement (that is, in the line printing direction).
The ink jet head units 10(n) (where n is an integer of one or more with only ink jet head units 10(1) and 10(2) shown in FIG. 13) are arranged in line as shown in FIG. 13 and bonded together end to end. The ink nozzles 11(m) (where m is an integer of one or more) arrayed in line in the line printing direction must be spaced with the same pitch p between every nozzle. The last and first (i.e., endmost) ink nozzles 11(128) and 11(1) in adjacent ink jet head units 10(1) and 10(2) must also be placed at this same pitch p. This means that the thickness of the wall separating the ink chambers communicating with the ink nozzles 11(1) and 11(128) at the ends of each ink jet head unit, that is, the adjacent end walls 12(1) and 12(128) of the ink jet head units, must be half the thickness of the wall separating the ink chambers communicating with the other ink nozzles.
Changing the wall thickness, however, means that the rigidity of the end walls is less than the rigidity of the other internal ink chamber dividers, and the ink discharge characteristic of the ink nozzles associated with these end ink chambers differs from the discharge characteristic of the other internal ink nozzles. This is undesirable because a difference in ink discharge characteristics lowers print quality.
Furthermore, as noted above the ink jet head units are bonded together at the outside of these end walls. This means that the end walls must be finished with good precision. This, however, makes manufacturing that much more difficult, and is thus undesirable.
These problems can be resolved by arranging the ink nozzles of the ink jet head units in a staggered pattern as taught in Japanese Unexamined Patent Application (kokai) 8-127137.
A problem with a staggered arrangement of ink nozzles in the ink jet head units is that positioning the inkjet head units to each other becomes more difficult. Imprecise alignment of the ink jet head units results in lower print quality, and is thus obviously undesirable. In addition, no method for precisely and easily aligning ink jet head units to each other has yet been proposed.
When using a staggered ink nozzle arrangement it is also necessary to adjust the ink nozzle drive timing between ink jet head units so that the ink drops ejected from different ink nozzles are placed on the same line on the print medium. Therefore, when the line ink jet head comprises a plurality of ink jet head units with a staggered ink nozzle array, the circuitry needed to adjust the drive timing is more complex compared with the drive circuitry of a line ink jet head having the ink nozzles in a straight line.